A storage apparatus retains a large-capacity storage area in order to store large data. A data amount increases year after year. Large data needs to be efficiently stored because of problems of the size and the costs of the storage apparatus. Therefore, in order to suppress the increase in the data amount stored in the storage area and increase data volume efficiency, de-duplication processing for data for detecting and eliminating duplication of data attracts attention.
The de-duplication processing is a technique for, when data (write data) to be written in a storage device anew is the same as data already stored in the storage device, managing only information such as a pointer to the already-stored data without writing the duplicate data in the storage device. Whether the write data is the same as the data already stored in the storage device is verified using, for example, hash values of the data.
Conventionally, a system for performing the de-duplication processing on the background after storing all data from a host apparatus in a disk (hereinafter referred to as post-process system as well) is adopted. However, in the post-process system, since all the data from the host apparatus needs to be written in the disk once, a large capacity storage area is necessary. Therefore, a technique for executing the de-duplication processing using not only the post-process system but also a system for performing the de-duplication processing before writing data in the disk (hereinafter referred to as inline system as well) is disclosed (e.g., PTL 1).